Absorption in calves of amoxicillin, ampicillin, and oxytetracycline given in milk replacer, water, or an oral rehydration formulation.

Oxytetracycline, amoxicillin or ampicillin suspended in milk replacer, water, or a glucose-glycine-electrolyte solution (GGES) was orally given to calves (n = 64). Oxytetracycline suspended in milk replacer gave lower relative bioavailability than when suspended in water (P less than 0.01) or in GGES (P less than 0.001). Seemingly, the 63% binding (only partly reversible) of oxytetracycline suspended in milk replacer was responsible for low serum concentrations, whereas the greater water absorption from the GGES was responsible for improved uptake of antibiotic. Amoxicillin suspended in milk replacer had a delayed absorption, compared with that suspended in water, but the relative bioavailabilities from milk replacer and water were similar. In contrast, peak serum concentration and bioavailability were higher (P less than 0.05) when amoxicillin was suspended in GGES than when suspended in water. Binding of amoxicillin with milk replacer was comparatively low (16%) and was reversible. Ampicillin suspended in GGES gave a higher peak serum concentration (P less than 0.05) than when suspended in milk replacer. It, therefore, appeared that these antibiotics were more bioavailable when suspended in GGES than when suspended in water or especially in milk replacer. Oxytetracycline was bound particularly strongly to milk replacer.